1. Field of the Invention
The present invention relates to a foreign matter inspection apparatus for a substrate and, more particularly, to an apparatus for detecting foreign matter attached to the surface of a substrate (e.g., a large-scale substrate such as a mask used in the manufacture of liquid crystal devices) on which patterns are formed.
2. Related Background Art
In a conventional foreign matter inspection apparatus, a light beam emitted by, e.g., a laser light source is deflected in a predetermined direction by a scanner such as a galvano mirror, a polygonal mirror, or the like, and is focused on the surface of a substrate via an f-.theta. lens or fsin.sup.- .theta. lens. With this operation, a linear scan line is formed across almost the total width of the substrate (almost the entire substrate in the scan direction) on the surface of the substrate to be inspected. Furthermore, the entire surface of the substrate is two-dimensionally scanned with the light beam by moving the scan line (light beam) relative to the substrate in a direction perpendicular to the scan line.
As described above, in the conventional foreign matter inspection apparatus, the linear scan line is formed on the surface of the substrate via the f-.theta. lens or fsin.sup.-1 .theta. lens. Therefore, when the size of a substrate to be inspected becomes large, the field angle required for the f-.theta. lens or fsin.sup.-1 .theta. lens increases. In order to obtain a large numerical aperture (NA) at such large field angle, the required lens diameter increases, resulting in high cost.
Also, as described above, the conventional foreign matter inspection apparatus uses the galvano mirror, polygonal mirror, or the like as a beam deflector required for forming the linear optical scan line. However, since the upper limit of the scan frequency of the galvano mirror is determined due to its reciprocal movement, the inspection speed is limited. On the other hand, it is difficult for the polygonal mirror to attain ideal optical performance since it is very difficult to attain plane tilt correction among planes.